import sys
def run(a,b):
if a < 3:
if a == 2:
return b+1
return b
b = a//3 + b
a = a//3+a%3
return run(a,b)
for line in sys.stdin:
_a = line.strip()
if _a != "0":
print(run(int(_a),0))
import sys
def run(a,b):
if a < 3:
if a == 2:
return b+1
return b
b = a//3 + b
a = a//3+a%3
return run(a,b)
for line in sys.stdin:
_a = line.strip()
if _a != "0":
print(run(int(_a),0))